The present invention relates to a charge air cooler and particularly to a pre-cooling device for the air, before the air passes through a cooling device.
The amount of air which can be supplied to a supercharged combustion engine in a vehicle depends on the pressure of the air but also on the temperature of the air. Supplying the largest possible amount of air to a supercharged combustion engine entails cooling compressed air in a charge air cooler before it is led to the combustion engine. The charge air cooler is usually situated in front of the conventional radiator in a vehicle. A charge air cooler usually comprises two tanks and a cooler portion with a plurality of tubular elements arranged in parallel which connect the tanks to one another. The parallel tubular elements are arranged at a distance from one another so that surrounding cold air can flow between the tubular elements and cool the compressed air in the tubular elements. A well-dimensioned charge air cooler can cool the compressed air to a temperature more or less corresponding to the temperature of the surrounding air.
To reduce emissions, there is a trend towards increasingly powerful supercharged diesel engines. The air led to a powerfully supercharged diesel engine is compressed to a higher pressure, which also causes the temperature of the air to rise. The result is more exacting requirements for the charge air cooler which has to cool the compressed air before it is led to the diesel engine. The tubular elements which lead the compressed air in the cooler portion of a conventional charge air cooler are usually made of aluminium. A charge air cooler of relatively small dimensions made of aluminium can have a high cooling capacity, because aluminium is a material with very good heat transfer characteristics. However, the strength of aluminium decreases at high temperatures. In cases where the air is compressed to such a pressure as to reach temperatures exceeding 250° C. it is usually not possible to use aluminium as material for the tubular elements.
One possibility is to make the tubular elements of charge air coolers of an alternative material, e.g. steel, which has a higher strength at high temperatures. However, such alternative materials usually have inferior heat-conducting characteristics to those of aluminium and are usually also heavier. Charge air coolers made of such alternative materials will therefore occupy significantly more space and be more expensive to make.
GB 2 023 797 refers to a supercharged combustion engine in which compressed air is cooled in two steps before being led to the combustion engine. As a first step, the compressed air is cooled in a first heat exchanger by the coolant which also cools the combustion engine. As a second step, the compressed air is cooled in a second heat exchanger by surrounding air. The two heat exchangers are mounted on one another so that the compressed air is led directly from the first heat exchanger to the second heat exchanger.